1. Field of the Invention
The present invention relates to a pretreatment liquid for a recording material and an image recording method using the pretreatment liquid.
2. Discussion of the Background
Recently, inkjet printers have been used very popularly because of being quiet and having low costs. In addition, color inkjet printers which can print color images on a plain paper have also been practically used in the market.
As colorants for inks for office-use inkjet printers, dyes which have high solubility, have been typically used to prevent occurrence of a nozzle-choking problem in that a nozzle of an inkjet printer is choked with a material such as colorants included in an ink. However, dyes typically have poor resistance to water and light. Therefore inks including a pigment as a colorant have been increasingly used for posters whose images are needed to have good resistance to water and light.
In addition, when color images are printed on a plain paper, an additive such as surfactants is typically used for inks to improve the penetration property of the inks, i.e., to improve blurring of the boundary portion between two or more overlaid color images (hereinafter this blurring is referred to as the image blurring problem). This technique is disclosed, for example, in Japanese Laid-Open Patent Publication No. (hereinafter referred to as JOP) 55-65269. However, even when such inks are used, a feathering problem in that character images and fine line images are blurred cannot be fully solved. Therefore a technique in which an ink having a low penetration property is used for only the black ink in a color ink cartridge is disclosed. However, by using such a technique, the feathering problem cannot be fully solved, and particularly the image blurring problem cannot be fully solved.
In attempting to solve such a problem, JOPs 56-86789, 55-144172, 55-81992, 52-53012 and 56-89594 have disclosed techniques in which a material capable of fixing a dye included in recording inks is previously coated on a recording material or a white pigment or a water-soluble polymer is coated on the surface of a recording material, to fix a dye ink image formed on the recording material. In these techniques, it is needed to use papers which have been subjected to a special treatment.
JOP 56-89595 discloses an inkjet printing method in which a solution of a polymer such as carboxymethyl cellulose, polyvinyl alcohol and polyvinyl acetate is sprayed on a surface of a plain paper and then an ink is sprayed to form an ink image on the polymer-coated area of the plain paper. However, the feathering problem cannot be prevented by such an image forming method, and in addition, the water resistance of the recorded images cannot be improved at all.
JOPs 64-63185, 8-20159 and 8-20161 have disclosed inkjet printing methods in which a pretreatment liquid including a compound capable of insolubilizing a dye included in an ink to be used for printing images is sprayed by an inkjet printing method on a surface of a recording material and then the ink is sprayed on the surface of the recording material. However, these methods have a drawback in that the pretreatment liquid is needed to have a low viscosity to be stable sprayed on the surface of a recording material, namely the content of the dye-insolubilizing compound in the pretreatment liquid has to be decreased, and thereby the image quality improving effect is hardly exerted.
In order to fully exert the image quality improving effect by using such a pretreatment liquid, it is needed to apply a large amount of a pretreatment liquid on a recording material, resulting in occurrence of problems such as curling or cockling of the recording material. In particular, image areas in which two or more color ink images are overlaid include a large amount of water, and therefore an ink-penetrating problem in that the ink images penetrate into a recording material and reach the backside of the recording material occurs as well as the cockling problem of the recording material.
JOP 8-142500 discloses an inkjet printing method in which a colorless liquid including a silicone compound such as silicone oils and a cationic compound is previously coated on a recording material and then a recording ink including an anionic compound is sprayed on the recording material to form an image thereon. However, the silicone-coated surface of the recording material has poor ink permeability and therefore it takes a long time to dry the recorded ink images. In addition, when an image is recorded on such a recording material at a high speed, various problems tend to occur. For example, problems occur such that a dot image tends to be mixed with the neighboring dots because the silicone-coated surface has poor wettability and an undesired white line image is formed in a solid image because a roller contacts the solid image which have not yet dried. Thus image qualities seriously deteriorate. In addition, when such a pretreatment liquid is preserved for a long period of time, the silicone oil included therein decomposes or is separated from the other components, and thereby images having good image qualities cannot be stably produced.
JOP 10-250216 discloses an image recording method in which a colorless or pale-colored record-accelerating liquid including a dye-insolubilizing compound capable of insolubilizing the dye included in a recording ink is applied on a surface of a recording material and then the recording ink is sprayed on the surface of the recording material, wherein the record-accelerating liquid further includes a specific surfactant. According to this image recording method, the surfactant in the record-accelerating liquid improves the permeability and wettability of recording materials, and thereby the recorded images can be rapidly dried, resulting in performance of high speed printing. However, there is a possibility that the colorant in the ink penetrates into the recording paper, resulting in decrease of image density and occurrence of the feathering problem. Therefore, the image recording method is needed to be further improved.
JOP 2000-37942 discloses an image recording method in which a pretreatment liquid including a water-soluble polyvalent metal salt or a polyallylamine in an amount of from 20 to 25% by weight is applied on a surface of a recording material by an inkjet printing method, and then an ink including a pigment as a colorant is sprayed after the recording material applied with the pretreatment liquid is pressed or heated, to form an image on the surface of the recording material. It is described therein that images having good image qualities can be formed on a recording material even when the pretreatment liquid is applied in an amount of {fraction (1/10)} to xc2xd of the application amount of a pretreatment liquid in conventional methods including no pressure applying process. In addition, it is also described therein that by pressing a recording material, occurrence of the cockling problem can be prevented. However, in this method an additional process such as pressing processes or heating processes has to be performed, and therefore the printing devices become complex and large in size.
JOPs 11-10856, 2000-44855 and 2000-63719 have disclosed pretreatment liquids including a water-soluble poly-valent metal salt in such a large amount as 35% by weight. These pretreatment liquids are applied on a surface of a recording material by an on-demand inkjet printing method, and therefore the pretreatment liquids have to have a low viscosity. As mentioned above, when pretreatment liquids having a low viscosity are applied on a surface of a recording material, the pretreatment liquid produces little image-quality enhancing effect. In addition, these pretreatment liquids is needed to include a special material such as particulate polymers which typically have high manufacturing costs.
Thus, an inkjet printing method by which images having high image qualities can be recorded at a high recording speed has not yet been realized although various proposals have been made.
Accordingly, an object of the present invention is to provide an image recording method by which images having fine line reproducibility, color reproducibility, and high water resistance can be formed without causing the image blurring problem.
Another objects of the present invention is to provide an image recording method by which images having high image density can be formed on both sides of a plain paper without causing the curling problem, cockling problem and ink-penetrating problem.
Yet another method of the present invention is to provide a pretreatment liquid to be applied on a surface of a recording material to form high quality image on the recording material using an inkjet printing method.
Briefly these objects and other objects of the present invention as hereinafter will become more readily apparent can be attained by an image recording method including the steps of applying a pretreatment liquid on a surface of a recording material; and discharging a recording ink, which includes a solvent and a component dispersed or dissolved in the solvent, on the pretreatment liquid on the surface of the recording material according to image signals before the pretreatment liquid has dried, to form an ink image on the recording material, wherein the pretreatment liquid includes a compound in an amount of 10 to 80% by weight, which depresses at least one of the dispersibility and solubility of the component in the recording ink and wherein the pretreatment liquid has a viscosity of from 10 to 10,000 mPaxc2x7s at 25xc2x0 C.
At this point, the passage xe2x80x9cthe pretreatment liquid has driedxe2x80x9d means the pretreatment liquid applied is solidified after the liquid components therein have evaporated, and does not mean that the pretreatment liquid applied on a recording material appears to be dried at glance because of being absorbed in the recording material.
It is preferable that the material is a colorant of the recording ink, and the viscosity is from 20 to 10,000 mPasxc2x7s at 25xc2x0 C.
In addition, it is preferable that the coating weight of the pretreatment liquid applied on the recording material is from 0.5 to 10 g/m2. The contact angle of the recording ink against the recording material which has been applied with the pretreatment liquid is preferably not greater than 90xc2x0. Further it is preferable that the surface tensions of the pretreatment liquid and the recording ink are from 40 to 60 mN/m and from 20 to 40 mN/m, respectively.
The pretreatment liquid may be coated on an area of the surface of the recording material other than the areas on which an image is to be formed by the recording ink.
When the pretreatment liquid applying step is performed, an applicator, which applies the pretreatment liquid on the recording material while touching the surface of the recording material, is preferably used. The applicator is preferably a roller.
It is preferable that the image recording method further includes a step of heating the applied pretreatment liquid before the pretreatment liquid is dried.
The recording material preferably includes pulp fibers and has a sizing degree not less than 10 s and an air permeability of from 5 to 50 s.
It is preferable that the recording ink includes an anionic compound or the material in the recording ink is anionic. The anionic compound or the anionic material is preferably selected from the group consisting of anionic dyes, pigments or dyes dispersed by an anionic dispersant, pigments modified by an anionic group and anionic color particulate materials.
As another aspect of the present invention, a pretreatment liquid is provided for an inkjet recording method in which an ink image including at least a solvent and a component, such as colorants, dispersed or dissolved in the solvent is formed on a recording material. The pretreatment liquid includes a compound in an amount of 10 to 80% by weight, which depresses at least one of dispersibility and solubility of the component in the recording ink, wherein the pretreatment liquid has a viscosity of from 10 to 10,000 mPaxc2x7s at 25xc2x0 C.
The pretreatment liquid is preferably colorless or pale-colored, and the viscosity thereof is preferably from 20 to 10,000 mpasxc2x7s.
The solvent preferably includes a water-soluble organic solvent in an amount of from 5 to 70% by weight based on total weight of the pretreatment liquid. The solvent preferably includes water in an amount of from 5 to 80% by weight. It is preferable that the pretreatment liquid further includes a water-soluble liquid compound and the solvent includes water, wherein the water-soluble liquid compound and water are included in the pretreatment liquid in an amount of from 20 to 80% by weight based on total weight of the pretreatment liquid. Preferably the content of water is not greater than 40% by weight, and the content of the water-soluble liquid compound is from 20 to 80% by weight. It is preferable that the content of water in the pretreatment liquid is not greater than the equilibrium water content of the water-soluble liquid compound at 60% RH.
The compound depressing at least one of dispersibility and solubility of the component in the recording ink is an ionic compound. The ionic compound preferably has an alkyl group having not less than six carbon atoms. The ionic compound is preferably an ionic polymer compound.
The ionic compound is preferably a cationic compound, and more preferably a cationic polymer. The cationic polymer preferably has one of the following formulae (1) to (18): 
wherein Xxe2x88x92 represents a halogen ion, a nitrate ion, a nitrite ion or an acetate ion; R represents an alkylene group having from 1 to 3 carbon atoms; and n is an integer (i.e., polymerization degree); 
wherein n is an integer (i.e., polymerization degree); 
wherein Xxe2x88x92 represents a halogen ion, a nitrate ion, a nitrite ion or an acetate ion; R1 represents a hydrogen atom or a methyl group; R2, R3 and R4 independently represent a hydrogen atom or an alkyl group; and n is an integer (i.e., polymerization degree); 
wherein Xxe2x88x92 represents a halogen ion, a nitrate ion, a nitrite ion or an acetate ion; and n is an integer (i.e., polymerization degree); 
wherein n is an integer of from 5 to 30; 
wherein n is an integer (i.e., polymerization degree); 
wherein Xxe2x88x92 represents a halogen ion, a nitrate ion, a nitrite ion or an acetate ion; and n is an integer (i.e., polymerization degree); 
wherein n is an integer (i.e., polymerization degree); 
wherein Z and Y independently represent xe2x80x94OCOCH3 or xe2x80x94OH; R5 represents an alkylene group having from 1 to 4 carbon atoms; and n, k and m independently an integer; 
wherein R6 represents an alkyl group; Xxe2x88x92 represents a halogen ion, a nitrate ion, a nitrite ion or an acetate ion; and n is an integer (i.e., polymerization degree); 
wherein R7 and R8 independently represent a hydrogen atom or an alkyl group; Xxe2x88x92 represents a halogen ion, a nitrate ion, a nitrite ion or an acetate ion; and n is an integer (i.e., polymerization degree); 
wherein Xxe2x88x92 represents a halogen ion, a nitrate ion, a nitrite ion or an acetate ion; and n is an integer (i.e., polymerization degree); 
wherein Xxe2x88x92 represents a halogen ion, a nitrate ion, a nitrite ion or an acetate ion; and n is an integer (i.e., polymerization degree); 
wherein j and k are independently an integer of from 2 to 6; and n is an integer (i.e., polymerization degree); 
wherein Xxe2x88x92 represents a halogen ion, a nitrate ion, a nitrite ion or an acetate ion; and n is an integer (i.e., polymerization degree); 
wherein Xxe2x88x92 represents a halogen ion, a nitrate ion, a nitrite ion or an acetate ion; Q represents another repeating unit of the copolymer; and n and m are independently an integer (i.e., polymerization degree); 
wherein Xxe2x88x92 represents a halogen ion, a nitrate ion, a nitrite ion or an acetate ion; and n is an integer (i.e., polymerization degree); and
The cationic compound is preferably a polymer having the following formula (18): 
wherein Xxe2x88x92 represents a halogen ion, a nitrate ion, a nitrite ion or an acetate ion; and n is an integer (i.e., polymerization degree).
The cationic polymer is preferably a cationic polymer including at least one of a repeating unit having the following formula (19) and a repeating unit having the following formula (20): 
wherein D1 represents a substituent having one of the following formulae (21) and (22); D2 represents a hydrogen atom or a substituent having one of the following formulae (21) and (22); n and m are independently an integer.
xe2x80x94CR9R10xe2x80x94PO3R11R12xe2x80x83xe2x80x83(21)
xe2x80x94CR9R10xe2x80x94SO3R11xe2x80x83xe2x80x83(22)
wherein R9 and R10 independently represent a hydrogen atom, an alkyl group having from 1 to 12 carbon atoms or an allyl group; R11 and R12 independently represent a hydrogen atom, an alkali metal or a substituent having the following formula (23).
xe2x80x94NR13R14R15R16xe2x80x83xe2x80x83(23)
wherein R13 to R16 independently represent a hydrogen atom, an alkyl group, an allyl group, a hydroxyalkyl group or a benzyl group.
The above-mentioned cationic compound may be particles dispersed in the pretreatment liquid. The particles are preferably a cationic silica or a cationic emulsion.
The material in the pretreatment liquid which depresses at least one of dispersibility and solubility of the component in the recording ink is preferably a water-soluble polyvalent metal salt.
The pretreatment liquid preferably includes at least one of a surfactant and a wetting accelerator so as to have a surface tension not greater than 40 mN/m.
The surfactant preferably has one of the following formulae (24) to (29). 
wherein R17 represents a lauryl group, a stearyl group or a myristyl group; 
wherein R18 and R19 independently represent an alkyl group having not less than 3 carbon atoms which may be branched; M represents an alkali metal, an ammonium group, an alkanol amine group, a quaternary ammonium group or a quaternary phosphonium group; 
wherein R20 and R21 independently represent an alkyl group having from 5 to 7 carbon atoms; and m is an integer of from 5 to 20; 
wherein R22 represents a carbon chain having from 6 to 14 carbon atoms which may be branched; and n is an integer of from 5 to 20; 
wherein m and n are independently 0 or an integer of from 1 to 20; and 
wherein R23 represents a carbon chain having from 6 to 14 carbon atoms which may be branched; and m and n are independently 0 or an integer of from 1 to 20.
The surfactant is preferably included in the pretreatment liquid in an amount of from 0.1 to 10% by weight based on total weight of the pretreatment liquid.
The pretreatment liquid preferably includes an antiseptic agent or antimildew agent in an amount of from 0.1 to 5% by weight.
In yet another aspect of the present invention, an image forming method is provided which includes discharging a recording ink according to image signals to form an ink image on a surface of the recording material on which a pretreatment liquid is applied and has dried, wherein the recording ink includes a solvent and a component dispersed or dissolved in the solvent, wherein the pretreatment liquid includes a compound depressing at least one of the dispersibility and solubility of the component in the recording ink in an amount of 10 to 80% by weight based on total weight, and
wherein the pretreatment liquid has a viscosity of from 10 to 10,000 mPaxc2x7s at 25xc2x0 C.
In a further aspect of the present invention, a recording material is provided which has on a surface thereof a dried pretreatment liquid, wherein the pretreatment liquid comprises a compound depressing at least one of the dispersibility and solubility of the component in the recording ink in an amount of 10 to 80% by weight based on total weight, and wherein the pretreatment liquid has a viscosity of from 10 to 10,000 mPaxc2x7s at 25xc2x0 C.
These and other objects, features and advantages of the present invention will become apparent upon consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.